The genotoxicity of crude substances cultured in Bacillus mojavensis KJS-3 (B. mojavensis KJS-3) was investigated by using Ames tester strains of Salmonella typhimurium (S. typhimurium) with or without metabolic activation (S9 mix). No increase in the number of revertants was observed in response to any of the doses of the culture supernatant fermented by B. mojavensis KJS-3 (5, 10, 50, 100, and 500 ${mu}g$/plate) in S. typhimurium TA 98, 100, 1535 and 1537 both in the absence and in the presence of S-9 metabolic activation system. The half-maximal inhibitory concentration ($IC_{50}$) value of the culture supernatant was >83.33 ${mu}g/mL$. Crude substances had no effect on the DNA repair system for mutagenesis. Furthermore, the cell number of S. typhimurium strains was observed to have decreased compared to the solvent control. These results showed dose-dependent activity on the mutagenicity of crude substances in Ames test. These results strongly indicate that antimutagenic compounds are produced during fermentation by B. mojavensis KJS-3. On using the Chinese hamster lung cell line in mammalian cell system, no clastogenicity of the culture supernatant fermented by B. mojavensis KJS-3 was observed in the absence or presence of the S9 mix at the concentrations of 1.66, 8.33, 16.67, and 83.33 ${mu}g/mL$. No significant increase in chromosome aberrations was observed in response to treatment with any of these concentrations, regardless of activation of the metabolic system. Consequently, the mutagenic potential of the culture supernatant was not induced with respect to in vitro bacterial reverse mutation and clastogenicity in the range of concentrations evaluated in these experiments in our study.